Capacitor Values Why so high? & What can I do?

[Skwiddy]

Hello,

I am currently modifying my Tube premamp. It's a AES / Cary AE3DJH that I built from scratch. The first version I built I tried to source exact values for the capactors spec. in the schematic. They all seem to be very high Voltage and uf. Why is this so? This makes replacing with 'high quality' caps impossible for me.

For example the output caps are rated at 5uf @ 400V. Why would I need to use a 400v rating on the output when at most it would be only a couple of volts? Could I use a lower voltage? 5uf @ 200v?

The other values seem quite high too? 2uf @ 400v on pin 5 of 6sn7.

10uf @ 400V x2 in power supply? (what happens if I go higher in value in cap in power supply?)

Another question while I am at it (if anyone knows) Can zener diodes be replaced with hexfreds? Does this yeild improvement?

Thanks for the help!

[mcs]

Originally posted by Skwiddy
For example the output caps are rated at 5uf @ 400V. Why would I need to use a 400v rating on the output when at most it would be only a couple of volts?

I don't have the schematic of you amp (if you post a link, that makes it a lot easier), but I guess the output cap is connected to either the plate or the cathode? I'm sure there's more than just a couple of volts there.

Could I use a lower voltage? 5uf @ 200v?

Perhaps. But are you sure the voltage never goes higher than 200V? Even during the tube warmup? But 5µF does sound high - 1-2µF should normally be fine.

The other values seem quite high too? 2uf @ 400v on pin 5 of 6sn7.

It may be high, but getting a 2µF 400V cap is no problem.

10uf @ 400V x2 in power supply? (what happens if I go higher in value in cap in power supply?)

Getting 10µF caps is no problem either. Use motor run caps for instance.

Another question while I am at it (if anyone knows) Can zener diodes be replaced with hexfreds?

No. Zener diodes are voltage references - hexfreds are rectifiers.

Best regards,

Mikkel C. Simonsen

[Skwiddy]

I don't have a digital version of the schematic. The rating that stumps me the most is the 5uf 400v for the output (it comes off of pin 6 of a 6sn7. Does this mean that my amp may see 400v from the preamp at times? While I have the schematic of the AE3 djh I have never looked inside of a real one. I don't know of many high end caps with 5uf 400v values. The ones I used where sprage...but I would like to upgrade them. Any thoughts?

I was also condsidering rebuilding my preamp with the power supply tube rectifier in a seperate case? Pros cons? Anyone think this is worth the effort?

[mcs]

Originally posted by Skwiddy
I don't have a digital version of the schematic. The rating that stumps me the most is the 5uf 400v for the output (it comes off of pin 6 of a 6sn7.

Pin 6 doesn't mean much, when you don't have the schematic

It could be a cathode follower. In that case the voltage is probably around half the supply voltage, so you probably need at least a 250V cap. If the tube shorts, you could have the full supply voltage on the output, so using a cap with a high voltage rating could be a good idea...

I don't know of many high end caps with 5uf 400v values. The ones I used where sprage...but I would like to upgrade them. Any thoughts?

How about the Solen caps? You can get caps up to 10µF, and up to 330µF at 250V...

Best regards,

Mikkel C. Simonsen